Netgear XCM8806 - 8800 SERIES 6-SLOT CHASSIS SWITCH 사용자 설명서

disable learning vlan <vlan-name>

Managing Egress Flooding

Egress flooding takes action on a packet based on the packet destination MAC address. By 
default, egress flooding is enabled, and any packet for which the destination address is not in 
the FDB is flooded to all ports except the ingress port.

You can enhance security and privacy as well as improve network performance by disabling 
Layer 2 egress flooding on a port or VLAN. This is particularly useful when you are working 
on an edge device in the network. Limiting flooded egress packets to selected interfaces is 
also known as upstream forwarding. 

Disabling egress flooding can affect many protocols, such as IP and 

ARP.

 illustrates a case where you want to disable Layer 2 egress flooding on specified 

ports to enhance security and network performance. 

In this example, the three ports are in an ISP-access VLAN. Ports 1 and 2 are connected to 
clients 1 and 2, respectively, and port 3 is an uplink to the ISP network. Because clients 1 and 
2 are in the same VLAN, client 1 could possibly learn about the other client’s traffic by sniffing 
client 2’s broadcast traffic; client 1 could then possibly launch an attack on client 2. 

However, when you disable all egress flooding on ports 1 and 2, this sort of attack is 
impossible, for the following reasons:

Broadcast and multicast traffic from the clients is forwarded only to the uplink port.

Any packet with unlearned destination MAC addresses is forwarded only to the uplink 

port.

One client cannot learn any information from the other client. Because egress flooding is 

disabled on the access ports, the only packets forwarded to each access port are those 
packets that are specifically targeted for one of the ports. There is no traffic leakage.

Client 1

Uplink
port 3

Access Link

port 2

Access Link

port 1

ISP FW/
Security Proxy

EXOS Switch
Access VLAN

XOS004A

Client 2